Self compensating control circuit

ABSTRACT

A temperature compensating control device for blankets, wall wire or outlet or fuse breaking devices, which incorporates solid on/off control. The use of solid on/off control with resistance temperature compensation sensors rather than a phase control renders the circuit free of &#39;&#39;&#39;&#39;gate trigger&#39;&#39;&#39;&#39; means normally associated with simplified thyristor circuits. This simplifies greatly the transistor stage gain or transistor shunt controls previously demonstrated in the art. Intrinsic simplification with fewer parts and solid state temperature resistance compensating means of the thyristor itself are innovative, besides requiring fewer parts. The circuits incorporates, preferably a temperature override electromechanical heat sensitive, fail safe control regulator and additionally in one aspect a double-stranded wire fail safe means for temperature responsive means. A thyristor SCR is incorporated in the circuit and functions in such a manner as to give snap on or off control.

0 United States Patent [151 3,679,872 Lauck, III [451 July 25, 1972 [54]SELF COMPENSATING CONTROL Primary Examiner-George Harris CIRCUITAssistant Examiner-F. E. Bell Attorney-J. Gibson Semmes [72] Inventor:Peter Lauek, II], Princeton, NJ.

[73] Assignee: Robert H. Myers, Washington, DC. a [57] ABSTRACT interestA temperature compensating control device for blankets, wall [22] Filed:Au 3, 1971 wire or outlet or fuse breaking devices, which incorporatessolid on/off control. The use d solid on/ofi control with re- [21] Appl.No.: 168,614 sistance temperature compensation sensors rather than aphase control renders the circuit free of gate trigger" means 52 us.0.... ..219/s01 normally associated with simplified thyristor circuitsThis [51] Int. cl. ..ll05b 1/02 i plifi gre ly the transistor stage gainor transistor shunt [58] Field of Search ..219/501, 504, 505, 212controls previously demonstrated in the art. Intrinsic simplificationwith fewer parts and solid state temperature resistance [56] ReferencesCited compensating means of the thyristor itself are innovative, besidesrequiring fewer parts. The circuits incorporates, UNITED STATES PATENTSpreferably a temperature override electromechanical heat 3,422,2441/1969 Lauck ..219/212 sensitive. fail safe tr l r gulator andadditionall in one 3,437,792 4/ 1969 Lauck.. ....219/505 aspect adouble-stranded wire fail safe means for temperature 3,544,767 12/1970Lauck..... ....219/50l responsive means. A thyristor SCR is incorporatedin the cir- 3,564,206 2/1971 Lauck ..219/501 cuit and functions in sucha manner as to give snap on or off control.

3 Drawing Figures .3 i sol W SCR 20 D PAIfNTEflJuLzsusm 3.679.872

SCR I5 20 9 l 26 ON SCR (SOLID) FIG. 2

30 J SCR 3 INVENTOR PETER LAUCK, HI

I g 1550/2 1mm ATTORNEY SELF COMPENSATING CONTROL CIRCUIT BACKGROUND OFTHE INVENTION 1. Field of the Invention The invention has particular usein applications utilizing heating devices in which activation of theheating element is controlled by a circuit including means acting as atemperature sensor and control activator for the heating device. Theinvention has a particular use in applications such as electricblankets, or other electrically heated fabrics or materials such aswoven or non-woven drapes, floor coverings, mobile home wall wiring andthe like, for better additional and different consumer protection thanthat presently provided. It also provides oil burner temperature controlwith fail safe receptacles or wall wire, wall outlet and fuse protectionfor overloaded conditions. It is commercially simplified also.

2. Description of the Prior Art The prior art discloses utilization ofheating devices in, for example, flexible blankets and heating devices,in which actuation of the heating element is controlled by temperaturecontrol sensors or actuators such as bi-metallic switches, thermostats,silicon controlled rectifier (SCR) circuits, thyristor circuits and thelike. Related inventions disclosing circuitry to which the presentinvention is applicable include:

P. Lauck, Ill U.S. Pat. No. 3,385,958 issued May 28, 1968 entitledELECTRIC BLANKET;

I. Lauck, III U.S. Pat. No. 3,422,244 issued .Ian. 14, 1969 entitledELECTRIC BLANKET WITH A TEMPERATURE RESPONSIVE CONTROL CIRCUIT;

P. Lauck, III US. Pat. No. 3,437,792 issued Apr. 8, 1969 entitledELECTRIC HEATING DEVICE WITH TEMPERA- TURE CONTROL MEANS;

P. Lauck, III U.S. Pat. No. 3,544,767 issued Dec. 1, 1970 entitledHEATING CONTROL CIRCUIT WITH SCR- UNIJUNCTION TRANSISTOR COMBINATION;

P. Lauck, III U.S. Pat. No. 3,548,157 issued Dec. 15, 1970 entitledHEATING CONTROL CIRCUIT WITH TRIAC- DIAC COMBINATION; and

P. Lauck, lII U.S. Pat. No. 3,564,206 issued Feb. 16, 1971 entitledFAILSAFE SENSOR/OVERRIDE FOR CIRCUIT Further comprising prior art is abasic half wave phase control circuit appearing in Fourth Edition GE SCRManual, pages 185-186. This latter utilizes phase control with a gatesemi-conductor trigger device (SUS) as well as other gate trigger meansas well as including a resistance potentiometer. The latter phasecontrol circuits do not result in control snap on/ofi' operation withoutany of many gate thyristor trigger means normally employed to avoidlatch" on or off instability, due to internal temperature build-up andconsequent resistance change within thyristor itself.

SUMMARY OF THE INVENTION The present invention is directed to a circuitfor use in electric blanket control and wall temperature controls whichprovide control snap on/off operation. The control is on/off SCR ratherthan a phase control and utilizes no potentiometer. The present controlfurther requires no gate semi-conductor trigger device (SUS etc). Thepresent circuit is for solid on/off control rather than phase control.Positive and negative temperature coefficient means are incorporatedwhich override the series and parallel configurations regulatorytemperature responsive means and are used with capacitive reactancecircuitry rather than a gate semi-conductor type of operation. Thecircuit configuration and components are highly efficient in operationand less costly than heretofore known with more complex stage gain orshunt circuits.

The invention, in one aspect, also incorporates a doublestranded wirewith two cores as a fail-safe for temperature responsive means whicheliminate use of costly bi-metallic elements in blankets and places oneor a plurality of temperature responsive means in the sleeping'areaand/or receptacle plug to provide a blanket or burner which is both safeand infinitely more sensitive than the present bi-metallic ambienttemperature control boxes and the like. 1

Additional objects and advantages of the invention will be more readilyapparent from the following detailed description of and embodimentthereof when taken together with the accompanying drawings in which:

FIG. 1 is a schematic circuit in accordance with the invention;

FIG. 2 is a wave diagram of a solid ON circuit condition; and

FIG. 3 is a view similar to FIG. 2 with a solid OFF circuit condition.

It is to be understood that the drawings disclose an illustrativeembodiment of circuits only, and the invention is in no way to berestricted thereto, since it is susceptible of broader application todifferent specific control circuits as referred to above, in patentedand pending patent application embodiments or others.

The illustrated circuit has been selected to disclose the basicprinciple of operation of the invention and those skilled in the art caneasily adapt this principle as illustrated to other circuits for thesame overall concept and operation.

In FIG. I, the heat control circuit of the present invention as shownincludes a conventional alternating current supply applied between inputterminals 10 and ll, 10 being the hot line and 11 the ground. Thecircuit includes, in series connection, a heating coil 14 in a usualmanner which is incorporated in the blanket or the like structure in anycurrently known fashion. Also, in series is an SCR which functions foron/off control rather than a phase control as in the GE circuit referredto as prior art. A voltage divider circuit includes a capacitor 18 whichis less costly than a potentiometer voltage current regulator and havinga different position from the said GE circuit. This circuit includesresistance 16 and temperature sensitive resistances, hereinaftersometimes called temperature sensors and thermistors," I2, 20, 21 and 22intermediate of which is an electromechanical switch 15. This switch 15is used in the voltage divider circuit and is not a gate operationsemi-conductor for an SUS, U'IT pulse transformer, diode, diac etc. Thecombination of the switch 15 and the negative temperature responsiveresistance 21 and the positive temperature responsive resistance 20provides a fail-safe control regulator as hereinafter explained.

The use of at least one negative temperature sensor 12 and a pluralityof negative and/or positive temperature sensors, or thermistors, 22, forwall wiring protection or blanket control is indicated. This control canconsist of a double stranded override wire having an inner core of thewire attached to the temperature responsive means sensors orthermistors. An insulating layer covers the inner core and thereabout isan outer core which preferably is made up of the continuity of theground line and/or other vital control area continued into the blanketin a plug of the receptacle and out of the other plug. As such, it is anextension of the third circuit ground line or other vital control meansinto the blanket and back to the control. Finally, around the outer coreis a polyvinyl chloride coating (PVC), the resulting double-strandedwire being located in the temperature sensing area and constituting afail safe part of the temperature responsive means. If the outer corebreaks, the heater coil continuity is interrupted and cuts off mainpower. Since the inner core connects to the temperature sensors and theouter core is a continuous ground circuit, the inner core in fact isprotected by a break in the outer core. It is impossible to have a breakin the inner core without breaking the outer core. Electric blankets andthe like in current use consist of bi-metallic thermostats but not solidstate temperature responsive sensor means. Rather, bimetallics in theprior art serve to open in case of an overheated condition but are notpositive temperature and negative temperature responsive regulators. Theuse of a double-stranded wire with two cores renders it possible toprevent thermal thyristor run away in the heretofore break of a solidstate negative temperature coefficient sensor. A break in the outer corewould thus automatically cut off the heater coil power.

This simple circuit constitutes a non-phase solid on/off control ratherthan phase control circuit as in the aforesaid GE circuit. The controlis on/oft thyristor SCR in that the control snaps on or ofi as opposedto the GE circuit. The circuit does not include a potentiometer and thecontrol has no gate semiconductor trigger device such as an SUS, etc.The miniature electro-mechanical screw adjusting temperature responsivemeans 15 is used here in conjunction with a capacitive reactance 18coupled with resistive voltage 16 and trigger voltage divider circuit,rather than a gate semi-conductor as referred to above.

The voltage is in a non-phase control, snap on/off circuit as can beseen from an examination of FIGS. 2 and 3. In FIG. 2, there is shown ano phase angle with the solid ON SCR indicated at'26 which is a solid Nnegative wave. The OFF thyristor SCR portion is indicated at brokenlines at 28. A solid OFF condition of the thyristor SCR is indicated inFIG. 3 at 30.

It is also to be noted that the capacitor 18 in this circuit isrepositioned with respect to the GE circuit and can be smaller and lesscostly than a potentiometer. Capacitive reactance coupled with resistiveand temperature resistive sensor means provides instant voltage andcurrent for triggering the thyristor SCR.

The invention also takes into consideration the fact that SOLID STATETHYRISTORS, SCR and TRIACS, and the like have the property of heating upand building up an internal thermal resistance when heated as opposed totheir normal inoperative temperatures. When such occurs the drift andthe settings of the parameters in the circuitry in which they are hookedchanges markedly. This, therefore, has heretofore necessitated amechanism called a gate trigger mechanism (SUS, DIAC, UNI-JUNCT IONTRANSISTOR, DIODES, NEON BULBS AND THE LIKE). In each case, thesetrigger mechanisms generate-enough voltage and current to trigger thegate of the thyristor SCR mechanism in such a manner that it reachessomewhere between its maximum and minimum forward voltage and currentratio to enable it to operate efficiently with dependability and lack ofdrift. Necessarily, this entails transistor amplifiers, differentialamplifiers, resistors, diodes, and often other mechanisms to insure thattheproper gate trigger mechanism operates at its assigned voltage suchas with Zener diodes.

An innovation of this new circuit in being self-compensating" is that ontop of the anode, or perhaps, the case which becomes very hot,particularly in the GE. circuit and in other thyristor units, there isplaced physically both a negative temperate coefficient temperaturesensor 21 and a positive temperature coefficient sensor 20. The negativetemperature coefficient sensor 21 and the peak reverse blocking voltageof most thyristors is in the area of volts. Since the negativetemperature coefficient thermistor or sensor 21 is connected across gateto ground of the SCR or thyristor itself, it is in parallel with itslike temperature sensing component 20 and components 12 and 22 in theblanket or other heating area (such as receptacle).

It is important to realize that the nominal resistance of a gate toground thyristor resister is about L000 olms. This register preventsreverse current and-voltage run away and consequent breakdown of thethyristor. The self-compensating means for an internally overheatedthyristor when in a "on" condition is described. The negativetemperature coefficient responsive means 21 works in conjunction with atleast one positive temperature coefficient responsive means 20.Temperature responsive means 20 is in a series-parallel electricalconfiguration as demonstrated in the drawing, FIG. 1. Temperatureresponsive means 20 and 21 also work in conjunction with temperatureresponsive means 12, 22. Temperature coefficient resistance curves ofthe positive and negative temperature sensitive means are predeterminedso that their steep resistive switching curves act in conformity withthe normal maximum and minimum operating specifications of the thyristorcurrent and voltage requirements as specified by the manufacturer. Sincenegative temperature responsive sensor 21 and at least one of thepositive coefiicient temperature responsive means, 20 or 22, should beof nominal olm value below 30 C and have little effect in the circuit atthese temperatures. At least one positive temperature coefficientresponsive means, 20, has a steep TCR and pronounced resistance increaseabove 30 C; thus, acting in conjunction with temperature responsivemeans 12 and 22 and other like sensor means 20 to prevent a heatedthyristor or other local area temperature build up by increasing theirresistance pronouncedly above a pre-set level. During such build up, thegate thyristor current is cut ofi, forcing said thyristor into an offcondition. The positive temperature coefiicient means 20, is mountedphysically in proximity to or on the anode, case or tab of thethyristor, and increases in resistance when the thyristor heats up. Itsincreased resistance, depending on its switching TCR curve, cuts downthe current flow of the thyristor gate current and works in conjunctionwith negative temperature coefficient sensor means 21. Sensor means 21is also mounted in proximity to the anode, case or tab of the thyristor.The temperature resistive switching curves of resistance sensor means21, 20, 12 and 22 are all different. Their electrical configurationcompensates for the normal area temperature operating mode as well as ahot thyristor with internal temperature build up. Temperature responsivemeans 22 and 12 are also selected so that when placed strategically inthe area of heated wire or heated area they also divide the current andvoltage to the thyristor shown in the drawings. They thereby dictate andregulate the on and off condition of the thyristor to a pre-set level.

At the same time, at least one positive coefficient temperature sensormeans 20 and negative temperatures coefi'icient temperature responsivemeans 21 work in conjunction with each other. They have differenttemperature resistive switching curves, however, which fundamentallychange little in resistance at normal operating modes of both the heatedareas as well as the thyristor itself. These different electricalresistance means have combinations of temperature responsive sensitivitywhich change their switching resistances drastically at temperatureabove 35 C. Whereas all temperature responsive means 12, 20, 21 or 22interact as demonstrated in the unique drawing, FIGS. 1, 2, and 3, theyoperate at different points of TCR, and interrelate in an innovativemanner so as to dictate an on and off" state of the thyristor and cutofi' said thyristor when either it or a heated area exceeds a presetlevel. Thus the temperature responsive means, all with differentresistive switching characteristics, maintain a balance,self-compensating condition in the heated area and thyristor itself.

Such a configuration as demonstrated in the drawing differs markedlyfrom the normally closed by-metallic element used in present seriesheater wire configurations alone. The latter do not compensate forthyristor build-up, or regulate blanket area temperature as is shownherein. This circuit controls the gate thyristor current and voltage,maintaining temperature stability in the local heater area as well ascompensating for the temperature in the thyristor itself. Suchtemperature stability is achieved by diflerent TCR curves of temperatureresponsive sensing means acting from a nominally low resistance at lowernormal operating temperatures to high, pronounced switching resistancesat the higher abnormal mode or temperatures.

Negative coefiicient temperature sensors 12 are constructed so as to behighly responsive within the potentially desired temperature range.These sensors 12 are electrically connected in parallel one to the otherand are physically placed throughout the area whose temperature is to beregulated. When the temperature falls below that desired, the negativecoefi'rcient temperature sensors 12 ,reach. such a value that so dividesthe voltages to trigger the thyristor SCR into an ON state. As thetemperature in the area to be regulated raises, the division of voltageschanges until the thyristor SCR is triggered into an OFF state.

Manifestly, minor changes in details of construction and arrangement ofparts and circuitry, within the teachings of the present invention canbe effected without departing from the spirit and scope of the inventionas defined in and limited solely by the appended Claims.

I claim:

l. In an electrical heating system and control circuit thereforincluding a heating element, capacitive resistance voltage dividercircuit means, at least one temperature responsive sensor and a heatingelement actuator, controllable by an in accordance with temperatureresponsive sensor to operatively energize and de-energize the heatingelement, the improvement comprising:

A. A series-parallel positioning of temperature responsive sensor meansassociated with said actuator and electrically connected in said voltagedivider circuit means; and

B. Said capacitive resistance voltage divider circuit means includingthe series connection of a capacitor and resistors operable to breakinput voltage to a reference voltage adapted to trigger said actuator insnap on and of? control.

2. A system as claimed in claim 1, said actuator comprising and SCRthyristor and said circuit having solid on" and solid off conditions,the solid on" of said SCR thyristor constituting a negative wave, saidsolid off SCR thyristor condition constituting a full sign wave.

3. A system as claimed in claim 2, said circuit voltage being a solidon/off control.

4. A system as claimed in claim 3, wherein at least one temperatureresponsive sensor is adapted to containment at the source of electricalenergy to comprise the heat control period.

5. The system of claim 3, the temperature responsive sensor comprising adouble layer coaxial wire, the outer layer of which contains the heatingelement, and the inner layer containing temperature responsive meanswhereby thermal run away of the thyristor is prevented in the event of abreak in the wire and failsafe condition is maintained.

6. In a system as claimed in claim 3 and including a double layercoaxial wire having an inner core attached to and forming a portion ofsaid temperature responsive means, an insulating layer over said coreand an outer layer being formed as a continuity of the control area inthe blanket and to the control therefor.

7. In a system as claimed in claim 6, said wire further including apolyvinyl chloride coating, functioning of said inner core beingunaffected by breakage of said outer layer whereby the inner core isoperable for control shut off.

8. A system as claimed in claim 1, said actuator comprising an SCRthyristor, a first positive and a first negative temperatureco-efficient temperature sensors connected to said SCR thyristor gatenode whereby internal solid state junction molecular change andtemperature build up during thyristor conduction is compensated.

9. A system as claimed in claim 8, said first positive and firstnegative coefficient temperature sensors connected to the gate node ofsaid SCR thyristor being physically located on or in proximity to saidthyristor.

10. A system as claimed in claim 8, comprising said first negative andsaid first positive coefiicient temperature sensors connected to thegate node of said SCR thyristor in parallel to at least onesecondnegative coefficient temperature sensor positioned physically in thearea where temperature is to be controlled.

LII

11. A system as claimed in claim 10, comprising at least one secondpositive coefficient temperature sensor connected electrically inparallel to said second negative coefficient temperature sensor andbeing positioned physically in the area where over heating is likely tooccur.

12. A system as claimed in claim 8, wherein said SCR thyristor, saidfirst positive and said first negative temperature coetficienttemperature sensors are grown together comprising a single componentintegrated chip or circuit.

1. In an electrical heating system and control circuit thereforincluding a heating element, capacitive resistance voltage dividercircuit means, at least one temperature responsive sensor and a heatingelement actuator, controllable by an in accordance with temperatureresponsive sensor to operatively energize and de-energize the heatingelement, the improvement comprising: A. A series-parallel positioning oftemperature responsive sensor means associated with said actuator andelectrically connected in said voltage divider circuit means; and B.Said capacitive resistance voltage divider circuit means including theseries connection of a capacitor and resistors operable to break inputvoltage to a reference voltage adapted to trigger said actuator in snap''''on'''' and ''''off'''' control.
 2. A system as claimed in claim 1,said actuator comprising and SCR thyristor and said circuit having solid''''on'''' and solid ''''off'''' conditions, the solid ''''on'''' ofsaid SCR thyristor constituting a negative wave, said solid ''''off''''SCR thyristor condition constituting a full sign wave.
 3. A system asclaimed in claim 2, said circuit voltage being a solid on/off control.4. A system as claimed in claim 3, wherein at least one temperatureresponsive sensor is adapted to containment at the source of electricalenergy to comprise the heat control period.
 5. The system of claim 3,the temperature responsive sensor comprising a double layer coaxialwire, the outer layer of which contains the heating element, and theinner layer containing temperature responsive means whereby thermal runaway of the thyristor is prevented in the event of a break in the wireand failsafe condition is maintained.
 6. In a system as claimed in claim3 and including a double layer coaxial wire having an inner coreattached to and forming a portion of said temperature responsive means,an insulating layer over said core and an outer layer being formed as acontinuity of the control area in the blanket and to the controltherefor.
 7. In a system as claimed in claim 6, said wire furtherincluding a polyvinyl chloride coating, functioning of said inner corebeing unaffected by breakage of said outer layer whereby the inner coreis operable for control shut off.
 8. A system as claimed in claim 1,said actuator comprising an SCR thyristor, a first positive and a firstnegative temperature co-efficient temperature sensors connected to saidSCR thyristor gate node whereby internal solid state junction molecularchange and temperature build up during thyristor conduction iscompensated.
 9. A system as claimed in claim 8, said first positive andfirst negative coefficient temperature sensors connected to the gatenode of said SCR thyristor being physically located on or in proximityto said thyristor.
 10. A system as claimed in claim 8, comprising saidfirst negative and said first positive coefficient temperature sensorsconnected to the gate node of said SCR thyristor in parallel to at leastone second negative coefficient temperature sensor positioned physicallyin the area where temperature is to be controlled.
 11. A system asclaimed in claim 10, comprising at least one second positive coefficienttemperature sensor connected electrically in parallel to said secondnegative coefficient temperature sensor and being positioned physicallyin the area where over heating is likely to occur.
 12. A system asclaimed in claim 8, wherein said SCR thyristor, said first positive andsaid first negative temperature coefficient temperature sensors aregrown together comprising a single component integrated chip or circuit.